There was a modest numeric increase in T1/2as well, but T1/2calculation was confounded by longer infusion times at the higher dose levels (up to 7h). MDX-447 + G-CSF (group 2). Hypotension was the predominant dose-limiting toxicity (DLT) in both treatment groups, with seven patients experiencing grade 3 events. MDX-447 half-life (T1/2) ranged from 1.9 to 8.4 h, with no obvious differences between the two NVS-PAK1-1 treatment groups. MDX-447 binding to neutrophils and peak levels of circulating tumor necrosis factor (TNF) and interleukin-6 (IL-6) were higher in group 2. The MTD for MDX-447 alone was 30 mg/m2. When NVS-PAK1-1 G-CSF was given with MDX-447, treatment was not well tolerated and group 2 was closed early because of safety concerns, with the last patient being treated at the 7 mg/m2dose level. There were no objective total or partial responses in either group. == Conclusion == MDX-447 alone was generally well tolerated, but did not accomplish objective tumor responses. The MTD for MDX-447 alone was 30 mg/m2weekly. Co-administration of G-CSF with MDX-447 precluded meaningful dose escalation. Keywords:Epidermal Growth Factor Receptor, Dose Level, Cetuximab, Maximum Tolerate Dose, Immune Effector Cell == Introduction == Bispecific antibodies are derived by linking two parental monoclonal antibodies or antibody fragments. The clinical therapeutic strategy with bispecific antibodies is usually to link immune effector cells to tumor cells directly. One antibody is usually directed against a NVS-PAK1-1 tumor antigen and the other antibody is directed against a cytotoxic trigger molecule, such as an Fc receptor, on immune NVS-PAK1-1 effector cells [1]. In comparison with standard monoclonal antibodies, bispecific antibodies may have enhanced ability to activate immune-mediated destruction of malignancy cells. MDX-447 is usually a bispecific antibody directed against the epidermal growth factor receptor (EGFR) and the high affinity Fc receptor (FcRI) [2]. EGFR is the prototypic member of the ErbB family of transmembrane receptor tyrosine kinases. EGFR is usually abnormally activated in many epithelial tumors including colorectal, head and neck, bladder, renal, non-small cell lung carcinoma, as well as others [3]. EGFR directed therapies have included antibodies directed against the cell surface receptor domain name and small molecule inhibitors of the intracellular tyrosine kinase domain name [3,4]. FcRI, a high affinity receptor for monomeric IgG, is usually expressed on monocytes, macrophages, immature dendritic cells, activated neutrophils, and other hematopoietic cells [5]. FcR1 helps mediate immune cytotoxic destruction of antibody-bound cells [6]. MDX-447 was created by cross-linking the humanized anti-EGFR monoclonal antibody (H425) F(ab) fragment and the humanized anti-FcRI (CD64) monoclonal antibody (H22) F(ab) fragment [2]. The parent anti-EGFR monoclonal antibody H425 has been administered systemically [7] and by intratumoral infusion [8] in two phase-I studies for NVS-PAK1-1 patients with glioblastoma multiforme. Systemic treatment was well tolerated, but intratumoral infusion was associated with significant toxicity attributed to local inflammatory reactions. No objective responses were seen in either study [7,8]. In an effort to improve the clinical efficacy of H425, MDX-447 was developed. In vitro studies have exhibited that MDX-447 binds to the EGFR and to FcRI both separately and simultaneously, and that the bispecific GCN5 antibody mediates antibody-dependent cellular cytotoxicity (ADCC) with lysis of EGFR overexpressing cell lines (R. Curnow, Medarex Inc., unpublished data). Maneuvers that up-regulate the activity of immune effector cells, such as simultaneous treatment with G-CSF, might enhance the cytotoxicity of bispecific antibodies. A bispecific antibody directed against FcRI and EGFR killed renal carcinoma cells in vitro more potently in the presence of peripheral blood from G-CSF treated donors, compared with peripheral blood from control donors [9]. In comparable experiments using a bispecific antibody against HER-2/neu and FcRI, destruction of breast carcinoma cells in vitro was enhanced in the presence of peripheral blood from G-CSF treated subjects, versus peripheral blood from control subjects [10]. The enhanced cytotoxicity observed in assays using G-CSF treated peripheral blood was thought to be due to, at least in part, the ability of.